Drift Prospecting
and Mineral Exploration


by Chad Seigel
November 2006


Table of Contents

1. Introduction 2. Methods used in drift prospecting 3. Dispersal trains 4. Summary 5. References






Introduction

During the last major glaciation, the Wisconsin, ice sheets covered most of Canada. These ice sheets scoured large areas of bedrock and transported this scoured material in a down ice direction where it was deposited as glacial sediments, most notably till. In some locations till contains minerals of economic value. Till such as this can be traced in an up ice direction to its source which may be a mineralized rock outcrop or till covered bedrock, this technique is known as drift prospecting.

Drift prospecting was originally developed in Finland, and was first researched in Canada in the 1950’s, since then it has been used extensively as an important mineral exploration tool. (GSC,2006). During the past few decades many valuable mineral deposits have been discovered such as copper ore, uranium, and most notably the Kimberlite deposit near Lac de Gras, Northwest Territories which is now a fully operational mine.

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Methods used in drift prospecting

Drift prospecting is not normally the only tool a geologist will use in the search for deposits of economically valuable minerals. Tools such as airborne and ground based geophysics as well as traditional prospecting methods are used in conjunction with drift prospecting to narrow down the search area. Once an area of interest is discovered, geologists search the ground for boulders and fragments of ore in till. (GSC, 2006). This is done by collecting samples at specific points along a field sample grid. These samples are carefully located in the field, mapped and labeled then sent to a lab for mineral and chemical analysis. When the results are interpreted they will hopefully show a pattern known as a dispersal train which is a plume of mineralized till in a down ice direction near the source of the mineral deposit.

A thorough understanding of Quaternary glacial geology is essential to the use of drift prospecting. Key factors such as ice flow direction, till thickness, and distribution of surface land forms are all used to determine the up-ice direction which will lead to the source of the mineral occurrence. The following statement emphasizes how important this understanding of Quaternary geology is. “Interpretation of results from summer field work led to the wrong assumption that a structurally controlled uranium-nickel deposit might exist in the boulder fields north of Zimmer Lake. To outline drilling locations an electro-magnetic survey was conducted which located several zones which were tested by a 19 hole drilling programme. No ore bearing intersections were obtained. An air photo study was then contracted to an experienced glacial geologist. An esker was recognized as being responsible for the transport of the ore boulders, which were located at the termination point of the esker. The conclusion was that the ore boulders originated from and area near Seahorse Lake, 5km north of the drilled area where the Gartner deposit was found.” (Gatzweiler, 1975).

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Dispersal trains

Dispersal trains are composed of material eroded from ore bodies and deposited by glaciers within a few kilometers of the bedrock source. There are five basic features common to most dispersal trains:

1) They are thin when compared to their length and width. Most are 0.5 to 10 km in length, 100 to 1000 m wide, and 1 to 5 m thick.

2) They are hundreds of times larger than their bedrock source.

3) They have sharp lateral and vertical contact with enclosing till.

4) They climb gently within the enclosing till, down ice from the source. The head may be buried with the tail reaching the surface.

5) Many dispersal trains show a down ice decrease in the concentration of ore components.

Some dispersal trains can be hundreds of kilometers in length. These trains pose a problem for prospectors, as exotics within the train from far a field can “wash out” material that may have come from sources in the local area, making it difficult if not impossible to locate the local source. An example of this is noted in the Fort Nelson area where Kimberlite indicator minerals have been noted through drift prospecting activities. These minerals may be from a local source, but may have also been carried from far to the east by the Laurentide ice sheet.





Plan and profile of a typical dispersal train showing mineralized outcrop covered by till. Image from Geological Survey of Canada, 2006


Map of a dispersal train showing down-ice movment of radioactive till near Allan Lake, Ontario. Mineralized outcrop at top ot dispersal train. Image from Geological Survey of Canada, 2006

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Summary

With a detailed understanding of Quaternary geology and local information such as direction of ice movement, number of glaciations, and till stratigraphy and lithology, drift prospecting can be a very useful tool. Geologists have used this method of prospecting in the past to locate ore bodies such as copper and uranium, and continue to use it in the search for new ore bodies such as Canadian diamond deposits.

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References

Aber, J.S. 2006. Earth Science 767 Quaternary Geology, Course Handouts. Emporia State University, Emporia, Kansas.

Bobrowsky, P.T. et. al.1995. Drift Exploration in the Canadian Cordillera. BC Geoligic Survey Paper 1995-2.

Campbell, J.E. 2006. Quaternary Geology of the Eastern Athabaska Basin: Implications for Uranium Drift Prospecting. Saskatchewan Geological Survey. Report 94-4.

Fulton, R.J. 1989. Quaternary Geology of Canada and Greenland. Geological Survey of Canada 839 pp.

Gatzweiler, R. et al,. 1975. Exploration of the Key Lake Uranium Deposits, Saskatchewan, Canada. Saskatchewan Geological Survey. Report 75-2.

Giangioppi, M., et al., 2003. Quaternary Glaciomarine Environments west of Committee Bay Central Mainland Nunavut. Geological Survey of Canada. Open File 4493.

Hambrey, M. and Alean, J. 2004. Glaciers. 2nd ed. Cambridge University Press. 376 pp.

Henderson, P.J. 1994. Surficial Geology Investigations Related to Drift Prospecting in the Annabel Lake – Amisk Lake Area, Saskatchewan. Saskatchewan Geological Survey. Report 94-4.

Kerr, D.E. 2001. Drift Prospecting Investigations in the Yellowknife Greenstone Belt, Northwest Territories. Geologic Survey of Canada. 2001-C1.


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This web presentation prepared for
Earth Science 767 ES 767 : Quaternary Geology
by Chad Seigel (November 2006)